Boosting the Photoresponse of Azobenzene Single-Molecule Junctions via Mechanical Interlock and Dynamic Anchor

As the most classic photoisomerization system, azobenzene has been widely utilized as a building unit in various photoswitching applications. However, attempts to build azobenzene-based single-molecule photoswitches have met with limited success, giving low on/off ratios. Herein, we demonstrate two designs of azobenzene-based photoresponsive single-molecule junctions, based on mechanically interlocked diazocine and azobenzene-based dynamic anchors, respectively. Molecular conductance measurements using the scanning tunneling microscope breaking junction (STMBJ) technique revealed dramatic conductance changes upon photoillumination, achieving a high on/off ratio of ∼3.7. Using density functional theory (DFT), we revealed peculiar quantum interference (QI) effects in the diazocine molecular switch, indicating that diazocine is an excellent candidate for molecular photoswitches. The asymmetric azobenzene devices with a dynamic anchor exhibit switching behavior between a fully off state and a highly conductive state associated with the trans/cis conformation transition. The findings of this work not only present the design and development of functional molecular devices based on azobenzene units but also provide insight into the fundamental properties of light-induced quantum interference in azobenzene-based molecular devices.